1. Technical Field
The present disclosure relates to imaging facial features. Specifically, the present disclosure relates to a focusing method for optically capturing an iris image.
2. Description of Related Art
Imaging of a human iris is often performed by illuminating a spatial volume that includes the face of a subject and then recording an image of an illuminated iris. Infra-red light is often used for illumination because pigmentation in the iris is more transparent in the infra-red spectrum. The transparency of the pigmentation exposes the fine structures of the iris to the imaging system.
Iris images are useful for performing biometric identification. Iris-based biometric identification typically requires a spatial resolution of 200 microns, or better, with a pixel resolution of approximately 60 microns for an ISO standard 19794-6-compliant image. In general, higher spatial resolution leads to better matching performance by better distinguishing the fine muscle structure of human irises.
Illumination systems used for iris imaging, particularly biometric imaging, regularly comprise multiple illumination sources that flood the ocular areas (i.e., the areas surrounding and including the eyes of the subject) with a uniform or near uniform intensity of light. This type of arrangement facilitates adequate illumination of the ocular area and any irises within the ocular area.
The figures depict various embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.